netdev - Re: Kernel panic when using bridge

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Date:	Tue, 12 Apr 2011 16:19:28 +0200
From:	Jan Lübbe <jluebbe@...ian.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Scot Doyle <lkml@...tdoyle.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Hiroaki SHIMODA <shimoda.hiroaki@...il.com>,
	netdev@...r.kernel.org
Subject: Re: Kernel panic when using bridge

On Tue, 2011-04-12 at 15:15 +0200, Eric Dumazet wrote: 
> Le mardi 12 avril 2011 à 15:02 +0200, Jan Lübbe a écrit :
> > Here you check dopt->optlen, which certainly should be 40 at most. The
> > calculation of dopt->optlen wasn't changed by my patch, though.
> 
> Check again the thread Jan.
> 
> Scot is using a tool (IP Stack Checker's tcpsic) to forge random tcp
> packets.

> Maybe your patch is fine but requires a change in a previous function,
> to make sure we deny some crazy packet before generating an ip_options
> with more than 40 bytes, in an icmp_send() reply.

One thing which could expose a problem is that it now will timestamp the
packet in the last 'slot', too. (which it didn't before)

In general, there is not a lot of error-checking in the options stuff.

> I took a look at this ip_options stuff and must say its really hard to
> even _read_ the code. Understanding it might need several days or a new
> brain ?

It took me some days do even figure out how it is supposed to fit
together...

> I cannot Ack or Nack your patch, I must admit it. Isnt it frightening?

David Miller already declared this code as 'officially terrible'...

Your patch should catch those forged packets before more harmful things
can go wrong, but even before my patch, i think forged packets could
cause trouble...

Regards,
Jan

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